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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

222
ALASKAN GLACIER STUDIES
of Disenchantment Bay and Russell Fiord, near Osier Island (Fig. 20) where the water is only 216 to 330 feet deep in contrast with depths of 500 to 800 feet near by in Russell Fiord and probable depths of 900 to 1000 feet in Disenchantment Bay. This may be regarded as a moraine rather than a place where the fiord was originally shallow (1) because of the suggestive slope of the mountain wall behind Osier Island, which should presumably descend as steeply below sea level as it does above, judging by other cross-sections of the fiord, and (2) because Hubbard and Variegated Glaciers are directly behind the shallow region and are still building up a deposit near by. This is being built up by direct discharge of the debris carried to the ice front of Hubbard Glacier, and by sediment from the streams beneath and at the margin of Hubbard, and from the Variegated and Orange Glacier streams whose great volume, muddiness, and visible deltas show how much detritus is being carried into the fiord. Beyond the ice front and the shore the floating icebergs axe also adding to the submarine deposits. The fiord is very shallow, certainly, as might be natural at the bifurcation of this valley where erosion is not concentrated. Unfortunately we do not know the depths in the uncharted waters of the west side of Hubbard Glacier and in front of the Haenke and Turner Glaciers. The moraine, if such it be, is somewhat abnormal in plan because built at the junction of two fiords and its surface shows nothing of the steep ice-contact feature of the
toys feet
FIG. 20.   CHOSS-SECTION or RUSSELL FIOED AT HUBBABD GLACTEB.   VERTICAL AND HOEIZONTAL SCALES
THH SAME.
supposed moraine near Nunatak Glacier, because the ice front has not yet retreated from it. The water is deepest in mid-fiord, as might be expected, but within a hundred yards of Variegated Glacier the water is 105 feet deep and increases rapidly westward. We do not regard it as demonstrated that this is a moraine rather than an originally shallow part of the fiord.
A third shoal, which pretty surely represents a moraine under water, lies about 7^ miles north of the head of Russell Fiord and is of especial interest because we had previously postulated a halt of the ice front of the expanded Russell Fiord Glacier at about this point, in connection with (a) overridden glacial gravels (b) the beaches of a marginal lake in the lower end of Russell Fiord.1 Both Russell and Gilbert recognized the evidence of this former lake2, and Gilbert detected the signs of overriding in the gravels.8 There should be a moraine at the junction of the southward limit of overridden gravels and the northward limit of the abandoned beach which were first shown upon a map in 1905; and just here the submerged moraine was found in 1910. The water is 828 feet deep atthis point and 1119 and 1044 feet on either side, so that the height of the submerged
 Tarr, R. S. and Martin, Lawrence, Bull. Amer. Geog. Soc., Vol. XXXVDI, 1908, pp. 163-4 and map facing p. 145; Tarr. R. S., Professional Paper 64, TJ. S. GeoL Survey, 1909, pp. 132-134, PI. XXXVII and Fig. 9.
"Russell, I. C., 18th Ann. Rept., U. S. Geol. Survey, 1892, pp. 88-89; Amer. Joura. Sci., 2nd Series, Vol. XT.TTT. 1892, p. 173.
* Gilbert, G. K., Harriman Alaska Expedition, Vol. HI, 1904, pp. 48, SI.